Cellulose fiber having improved biostability and the resulting products

ABSTRACT

A cellulose fiber having extended biostability and the method of its manufacture are described. While prior treatments of cellulose with biotoxic metal compounds have given improved resistance to decay, these treatments have not been entirely satisfactory where the fiber had to be refined before use. Refining energy was very high and fiber length loss was substantial. Treatment of cellulose fiber with dideyldimethylammonium chloride (DDAC) or bromide (DDAB), these materials in combination with low levels of copper, or low levels of copper alone, has given a product with very good biostability without a major increase in refining energy or loss of fiber length. The treated fiber is particularly advantageous as a reinforcing component for cement board products.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/228,815, filed Aug. 27, 2002, which is a continuation of U.S. patentapplication Ser. No. 09/838,947, filed Apr. 19, 2001, which claims thebenefit of U.S. Provisional Patent Application No. 60/199,344, filedApr. 24, 2000, priority from the filing dates of each is hereby claimedunder 35 U.S.C. § § 120 and 119, respectively. Each of theabove-identified applications is incorporated herein by reference in itsentirety.

FIELD OF THE INVENTION

The present invention is directed to a cellulose fiber having excellentresistance to environmental degradation, and to its method ofpreparation.

BACKGROUND OF THE INVENTION

Fiber reinforced cement board products used as building materials havebeen in service since the second decade of the 1900s. Portland cementserves as a matrix or binder for wood particles or strands. In turn, theparticles significantly reduce density and contribute strength,particularly tensile strength, to the product. Earlier products weremade using wood excelsior as a reinforcing material. Later, asbestosfiber was widely used as a reinforcing fiber. The fiber is intimatelymixed into a Portland cement-water slurry so that it is evenly coated.This mixture is predominantly formed into flat panels where the cementis allowed to cure before use. Alternatively, three dimensional productssuch as corrugated panels, roof tiles, and pipes can be made. Panels canbe made with varying densities. Low density products find interiorapplications as sound absorbent products for walls and ceilings. Higherdensity panels are used as flooring, siding, sheathing, and concreteforms. For many years asbestos reinforced simulated shingles were widelyused as siding for home construction. This application largelydisappeared after the health problems associated with asbestos wereuncovered. Today, cement board reinforced with cellulose fiber has madea significant comeback as a home siding product. In this application itsimulates horizontal or vertical wood siding. Although the productrequires special saws, it can otherwise be conventionally handled andnailed. Cement board siding is accepted as an attractive durable,dimensionally stable, low maintenance product resistant to moisture,decay, and insects.

Unbleached kraft pulps are predominantly used as the fiber source forcement board siding. Soroushian et al., in Inorganic-Bonded Wood andFiber Composite Materials, A. A. Moslemi ed., 3: 9-19 Forest ProductsSociety (1993) (hereafter IBWFCM), generally describe the process ofmanufacture and properties of the resulting products. Similarly,Soroushian et al., in IBWFCM., 5: 3-7 (1997), describe a process foraccelerated curing of the products by autoclaving in high pressuresteam. Detailed layouts of plants for fiber reinforced cement boardproduction are given by K. Buchmayer, IBWFCM 6: 99-140 (1998), and G.Agansky, IBFWCM 6: 141-146, (1998), (1998). Briefly a slurry of thecellulose fibers is formed. Separately a slurry of cement, filler, andother additives is prepared. These are mixed and formed into sheets orpanels, usually on an endless wire screen, where they are thendewatered. The dewatered panels are trimmed, pressed, and stacked. Theyare then autoclaved to accelerate hydration of the cement and induce atleast sufficient strength so that the panels can be handled withoutbreakage. Post curing and finishing are usually additional manufacturingsteps before the panels are shipped.

Today, the Hatschek wet process is the most widely used productionmethod. An aqueous slurry of fiber and cement with about 7-10% solids isformed into sheets on several rotating cylinders. Several thin layersare superposed until a panel of the desired thickness is formed. This isdewatered and cured as described above (see Concrete Technology aidDesign: Natural Fibre Reinforced Cement and Concrete, R. N. Swamy, ed.,Vol. 5, pp 23-25, Blackie, London). Typically about 10-30% by weight ofthe composite material will be refined cellulose fibers with the balancebeing inorganic mineral components.

The manufacturing environment for cement bonded panels is very highlyalkaline. As was noted, unbleached kraft fiber is frequently used asreinforcement. Two problems have been attributed to use of kraft fiber,one during manufacturing and one during use. The first is due toalkaline leaching of materials not removed from the fiber in the pulpingprocess. These materials are generally degraded lignin and carbohydrateresidues. When present in excessive amounts they interfere with thecuring process and can deleteriously affect strength of the finishedproduct. Under some use conditions the fiber is subject to biologicalattack also resulting in weakening the product.

The present inventors are aware that some previous consideration hasbeen given to control biological degradation of cellulosic reinforcementin cement board products. They would note that chromated copper arsenate(CCA) treated wood particles have been used. This use has not been withany intention of making biologically durable products but as a way ofdisposing of scrap or out-of-service CCA treated wood which is notsuitable for use as fuel (see Hsu IBFWCM 4: 3-5 (1995), and P. A. Cooperet al. IBFWCM 6: 340-348 (1998)). The authors concluded that CCA treatedred pine was useable when comminuted into particles and that the productcould be made so that leaching of the toxic materials was minor. Goodellet al., in Forest Products Journal 47(11/12): 75-80 (1997), exploredsubsoil decay resistance of three wood-cement composite materials. Theyconcluded that only wood particles in the surface regions would likelybe subject to fungal attack. Japanese Patent Application 4333611describes a cross linked acrylic fiber which may be made from monomersthat include multivalent metal acrylates. When the multivalent metals inthe fiber are copper or zinc the fibers have antibacterial properties.There was no suggested use of the fiber as a cement board reinforcement.Japanese Patent 11-181619 describes a polypropylene fiber useful incement boards. The fiber is resistant to autoclaving at temperatures ashigh as 170°-180° C. The fiber is melt spun with a zinc containingnucleating agent, said to contribute antimicrobial properties. JapanesePatent 3132552 describes a cement board fiber containing 3-40% woodfiber having high durability. The fiber is impregnated or coated with ametal compound selected from copper, zinc, aluminum or lead chloride orsulfate. Japanese Patent Application 288149/87 describes wood reinforcedcement boards in which a salt of iron, copper, lead, zinc, or aluminumis added to the mixing water. The salt is said to react with componentsleached from the wood chips and to prevent hardening retardation causedby the leachates. No mention was made of improvement in resistance tobiological degradation.

Canadian Patent 1,134,564 describes cellulose fibers which are treatedfor fungal resistance with metal oxide acylates in which the metal isselected from aluminum titanium, copper, zinc, antimony, chromium, iron,manganese, or zirconium. Alternatively, other organic and inorganicmetal compounds of copper, mercury, chromium, tin, and zinc were said tobe useful. The treated fibers are suggested for use as an asbestossubstitute in cement products, brake linings, gaskets, etc.

A significant problem with cellulose fibers treated with heavy metalbiocides is that they require a high energy input and are subject toconsiderable degradation during the refining process required for themanufacture of cement board products. The present invention hasaddressed and presents a solution to this problem.

SUMMARY OF THE INVENTION

The invention is directed to a fibrous cellulose product resistant tobio-logical degradation, and to the method of making the product. It hasbeen unexpectedly discovered that cellulose fiber treated with acompound selected from didecyldimethylammonium chloride (DDAC) orbromide (DDAB), DDAC or DDAB combined with small amounts of copper, orvery low levels of copper alone, offers excellent protection againstbiological deterioration when used as reinforcement in cement boardproducts. The fiber does not require significantly increased energyinput levels or have serious fiber length degradation during refining.The amount of the copper compound included is below that at whichsignificant interference with refining occurs.

DDAC and DDAB are useful in the range of 0.1%-2%, based on the dryweight of fiber present with 0.5%-1.0% being the preferred usage.Copper, as Cu based on weight of dry fiber, may be used in the range ofabout 0.01%-0.25% either alone or in combination with DDAC or DDAB. Thismay be added as any water soluble copper salt. The copper becomespermanently fixed on/in the fiber after exposure to the highly alkalineconditions encountered after mixing with Portland cement.

While an unbleached kraft fiber is a preferred raw material because ofits strength and cost, other chemically pulped cellulose fibers areknown to be equally suitable. These include bleached kraft pulps, andbleached and unbleached sulfite and semichemical pulps, such aschemithermomechanical pulps. When used as a reinforcement for cementboard products there is little incentive to use the more expensivebleached pulps even though their technical performance is equivalent tothe unbleached fibers.

The term “cement board products” should be read with sufficient breadthto include flat panels or strips, corrugated panels, and cellulose fiberreinforced cement pipe. These products include those used for siding,roofing and tile backer among many others.

It is an object of the invention to provide a cellulose fiber havingimproved biostability that may be refined without significantlyincreased energy input.

It is a further object to provide a biostable cellulose fiber that maybe refined without significant fiber length loss or fines generation.

It is another object to provide a biostable cellulose fiber particularlysuitable for the manufacture of cement board products.

These and many other objects will become readily apparent upon readingthe following detailed description of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Samples for testing were prepared by obtaining unbleached mixed coniferkraft pulp sheets produced in an interior British Columbia mill. Thesheets were essentially unrefined and had a basis weight of about 900g/m². Solutions of various biocides were made up so that the desiredultimate concentration of active material would be obtained by sprayingeach sample portion of pulp sheet with about 1 g of the biocidalsolution per gram of pulp. The treated sheets were then air dried to fixthe active ingredient. Subsequently the treated sheets were reslurriedin water having a pH ˜12 obtained from a cement board manufacturingfacility and refined to a Canadian Standard Freeness (CSF) level of 450mL. All refining was done in a pilot scale Model 202 Claflin refiner(available from Bolton-Emerson, Inc., Lawrence, Mass.). The treated andrefined pulp was dewatered by centrifuging to a consistency of about 30%and then pin fluffed to ensure uniformity.

Treatments included copper sulfate at concentrations of 0.1, 0.3, and0.5% Cu w/w based on dry pulp; zinc sulfate at concentrations of 0.1%,0.3%, and 0.6% Zn; 0.2% propiconazole emulsion; didecyldimethylammoniumchloride (DDAC) 0.2%, 0.5%; and 1.0%, and 1.0% DDAB. Treated fibers werealso made using 1.0% DDAC with 0.05%, 0.10%, and 0.2% Cu added as coppersulfate. All concentrations are on a weight/weight basis.

EXAMPLE 1 Examination of Samples for Biodurability

Samples of 30 g of the treated pulps were reslurried in water and formedinto sheets in an 8×8 inch (203×203 mm) sheet. The sheets were pressedto remove excess moisture then air dried. Each sheet was then cut inhalf and dipped for 30 seconds in a slurry of one part Portland cementin three parts by weight water. The coated and impregnated sheets wereremoved and drained, allowed to cure for two days wet, and then airdried. Each 4×8 inch (151×203 mm) cement treated sheet was then enclosedin a 20 mesh stainless steel screen and half buried in the ground at atest site at Hilo, Hi. Samples were then removed after three month, sixmonth, nine month, and twelve month periods for examination. Exposedsheets were assigned a subjective rating for deterioration based onvisual observation (3=sound and 0=complete deterioration). The exposedsheets were also examined microscopically to determine the presence offungal mycelium and cell wall deterioration. Results of these tests areseen in Tables 1, 2, 3, and 4. 1 TABLE 1 Results of 3 Months IngroundTesting Above Below Ground Ground Fungi Presence Sample Treatment RatingRating Above Ground Below Ground None 3 1 Yes - high Yes - low CUS04 -0.1% Cu 3 3 Yes - vy. low Yes - vy. low CUS04 - 0.3% Cu 3 3 No NoCUS04 - 0.5% Cu 3 3 Yes - vy. low No ZnS04 - 0.1% Zn 3 1 Yes - low Yes -medium ZnS04 - 0.3% Zn 3 1 Yes - low Yes - low ZnS04 - 0.6% Zn 3 1 Yes -low Yes - medium Propiconazole - 3 1 Yes - low Yes - medium 0.2% DDAC -0.2% 3 2 Yes - high Yes - med. high DDAC - 0.5% 2 2 No No DDAC - 1.0% 32.5 No Yes - vy. low DDAB - 1.0% 3 3 No No DDAC - 1.0% + 3 2.2 - - 0.05%Cu DDAC - 1.0% + 3 3 - - 0.1% Cu DDAC - 1.0% + 3 2.5 I - - 0.2% Cu

Rating of 3 indicates sound. Rating of 0 indicates completedeterioration. TABLE 2 Results of 6 Months Inground Testing Above BelowGround Ground Fungi Presence Sample Treatment Rating Rating Above GroundBelow Ground None 2 0 Yes - low No CUS04 - 0.1% Cu 3 1.5 Yes - vy. lowYes - high CUS04 - 0.3% Cu 3 3 No No CUS04 - 0.5% Cu 3 3 No Yes - vy.low ZnS04 - 0.1% Zn 3 1 Yes - vy. low Yes - med. high ZnS04 - 0.3% Zn 31.3 Yes - med. low Yes - med. low ZnS04 - 0.6% Zn 3 0.5 Yes - high Yes -med. high DDAC - 0.2% 2.8 0.5 — — DDAC - 0.5% 3 1 — — DDAC - 1.0% 3 2 —— Propiconazole - 3 0.5 Yes - vy. low Yes - low 0.2% DDAB - 1.0% 2 2.8Yes - vy. low Yes - vy. low DDAC - 1.0% + 3 0 — — 0.05% Cu DDAC - 1.0% +3 1 — — 0.1% Cu DDAC - 1.0% + 3 1 — — 0.2% Cu*Average of two tests. Rating of 3 indicates sound. Rating of 0indicates complete deterioration.

Based on the test conditions employed, effective below ground protectionwas given by copper at concentrations of 0.3% or greater; DDAB at 1%(lower concentrations not tested); and DDAC at 0.5% or greater. Additionof copper to 1.0% DDAC did not increase below ground protection at ninemonths. Zinc compounds or propiconazole at 0.2% did not give effectivedecay protection at any concentration tested. TABLE 3 Results of 9Months Inground Testing Above Below Ground Ground Sample TreatmentRating Rating None 1.5 0 CUS04 - 0.1% Cu 3 1.5 CUS04 - 0.3% Cu 3 2.3CUS04 - 0.5% Cu 3 2.5 ZnS04 - 0.1% Zn 2.3 0 ZnS04 - 0.3% Zn 3 0.8ZnS04 - 0.6% Zn 2 0 Propiconazole - 0.2% 2.8 0.5 DDAB - 1.0% 3 1.3DDAC - 0.2% 2.8 0 DDAC - 0.5% 2.5 0 DDAC - 1.0% 3.0 1.5 DDAC - 1.0% +0.05% Cu 2.3 0 DDAC - 1.0% + 0.1% Cu 3 0 DDAC - 1.0% + 0.2% Cu I 3 0*Average of two tests. Rating of 3 indicates sound. Rating of 0indicates complete deterioration.

TABLE 4 Results of 12 Months Inground Testing Above Ground Below GroundSample Treatment Rating Rating None 2.3 0 CUS04 - 0.1% Cu 2.3 0.5CUS04 - 0.3% Cu 2 1 CUS04 - 0.5% Cu 3 2.3 ZnS04 - 0.1% Zn 2 0 ZnS04 -0.3% Zn — — ZnS04 - 0.6% Zn 1.5 0 Propiconazole - 0.2% 2.3 0 DDAB - 1.0%— — DDAC - 0.2% — — DDAC - 0.5% — — DDAC - 1.0% — — DDAC - 1.0% + 0.05%Cu 2.8 0 DDAC - 1.0% + 0.1% Cu 3 0 DDAC - 1.0% + 0.2% Cu 3 0*Average of two tests. Rating of 3 indicates sound. Rating of 0indicates complete deterioration.

Only copper was effective in reducing cellulose fungal decay after theone year underground tests. It should be noted that burial in surfacesoil in a semitropical environment is a very severe accelerated agingtest. The only cement board product likely to experience such anenvironment would be pipe. However, the test should be indicative oflong term durability above ground. With the exception of samples treatedwith only copper, the DDAC and DDAB treated material performed as wellas any of the other treatments. This treated fiber offers significantadvantages in refining energy and fiber length retention as comparedwith copper, as will be seen in the following examples.

EXAMPLE 2 Claflin Refining Tests of Biocidally Treated Pulps

Refining tests were run in duplicate on pulp samples prepared as in theprevious example to determine energy input to constant freeness andevaluate the resulting fiber for damage. Refining times were adjusted toattempt to get a freeness of about 450 mL C.S.F. In addition to thesamples evaluated earlier, samples of DDAC with 0.05%, 0.10%, and 0.20%copper were tested. Results are given in Table 5. TABLE 5 Results ofClaflin Refining Tests Length Length Weighted Weighted Refining CS FiberFines Sample Energy, Freeness, Length, <0.2 mm, Treatment MJ/t mL mm %Untreated¹ 920 450 2.31 4.8 Zinc sulfate-0.1% Zn 960 450 2.31 5.0 Zincsulfate-0.3% Zn 970 500 2.21 5.2 Zinc sulfate-0.6% Zn˜ 1015 450 2.20 5.7Propiconazole - 0.2% 980 460 2.18 5.6 Copper sulfate-0.1% Cu 1060 4802.14 6.0 Copper sulfate-0.3% Cu 1410 470 1.61 8.0 Copper Sulfate-0.5% Cu2100 480 1.59 8.8 Untreated³ 1251 460 2.35 5.2 1% DDAC + 0.05% Cu 1340474 2.23 5.8 1% DDAC + 0.10% Cu 1480 450 2.12 5.8 1% DDAC + 0.20% Cu1960 465 1.98 6.7¹Average of four samples at different production times.²Average of three samples.³Different control and pulp sample for DDAC + Cu samples

While the two higher levels of copper gave good biological protection,it is immediately evident that the energy needed to refine them wassignificantly increased over the untreated material. Fiber damage wassignificant for the two higher levels of copper usage. The zinc andpropiconazole samples refined well but their biological protection waspoor. The use of up to 0.10% copper alone or with DDAC did not result inany major increase in required refining energy and did not causeunacceptable loss of fiber length.

EXAMPLE 3 Results of Bird Escher Wyss Refining Tests

Samples of the unbleached Canadian kraft pulp used in the earlier testswere made using 0.2% 0.5%, and 1.0% DDAC based on dry pulp weight. Acomparison sample was also made using a copper-chromium treatment with0.2% Cu and 0.35% Cr, based on dry pulp weight. This latter treatment isone used commercially for wood exposed to conditions causing decay. Thesamples were refined for this trial in a Model R 1 L Bird Escher Wysspilot plant scale refiner (available from Bird Escher Wyss, Mansfield,Mass.). Again the attempt was made to refine to a constant freenessvalue. The copper-chromium treated sample was inadvertently refinedsomewhat more heavily than desired. Energy consumption results are givenin Table 6. TABLE 6 Results of Escher-Wyss Refining Tests Length LengthWeighted Weighted Refining CS Fiber Fines Sample Energy, Freeness,Length, <0.2 mm, Treatment MJ/t mL mm % Untreated 2640 475 2.42 4.5Copper chromate - 0.2% 5440 320 2.06 6.0 Cu and 0.35% Cr DDAC - 0.2%2680 445 2.30 6.2 DDAC - 0.5% 2720 448 2.30 4.9 DDAC - 1.0% 2740 5002.31 5.2

As in the previous example, there was no serious increase in refiningenergy of loss of fiber length during refining in the DDAC treatedsamples. The copper-chromium treated sample required about double therefining energy of the other treated material. While some part of thisis due to the lower freeness of this sample, this does not begin toaccount for the great increase noted. It was also observed that therewas considerable leaching of the chromium from this sample.

Further tests have shown that the refined DDAC or DDAC plus coppertreated fiber have no inhibiting effect on the cure of concrete productsusing the fiber as reinforcement. The treated fibers handled normally inevery respect and were fully equivalent in manufacturing performance andproduct physical properties to untreated material. However, as noted inTables 1-3, durability under environmental conditions that might inducefiber decay was greatly improved for the DDAC treated fibers.

It will be apparent to those skilled in the art that many variations inthe preparation and use of the products of the invention could be madethat have not been described herein. It is the intention of theinventors that these variations should be included within the scope ofthe invention if encompassed within the following claims.

1. A cellulose fiber product resistant to biological degradation whichcomprises cellulose fibers derived from wood, the fibers initially beingat least partially purified by a chemical pulping process and containinga biocide consisting essentially of 0.01-0.25% by weight of dry fiber ofcopper from a water soluble copper salt, the fiber product beingresistant to fiber length degradation during refining.
 2. The cellulosefiber product of claim 1 which further includes in combination with thecopper salt a biocidally effective amount of a compound selected fromthe group consisting of didecyldimethylammonium chloride,didecyldimethylammonium bromide, and mixtures thereof.
 3. The cellulosefiber product of claim 2 in which the didecyldimethylammonium chloride,didecyldimethylammonium bromide, or mixture thereof is present in anamount of 0.1-2.0% by weight of dry fiber.
 4. The cellulose product ofclaims 1 or 2 in which the cellulose fiber is an unbleached kraft fiber.